Method for treating metal shapes



Jan. 14, 1941.

65/1/0/A/6 MOMENT E. C. ADAMS ETAL.

METHOD FOR TREATING METAL SHAPES Filed May 2,

Zlwuwvtom ERNEST C. ADA 75 ST/FP JOHN I? Patented Jan. 14, E941 UNITED STATES METHOD FOR TREATING METAL SHAPES Ernest C. Adams and John R. Stipp, Dieterich,

Ill., assignors of one-third to Cloyd M. Smith,

'Arlington, Va.

Application May 2, 1939, Serial No. 271,378

10 Claims.

This invention relates to a method for improving the mechanical properties of shaped or formed metal articles and is especially applicable for increasing the elastic limit and yield point of metal beams, girders, and the like, which are to be subjected to bending stresses in service.

Shaped metal articles such as beams which are used as girders are subjected while in use to high bending stresses in one direction and to but very little bending stress in. the opposite direction. In recent years the erection of large metal structures having long unsupported spans has created a demand for metal beams which have a high usable strength when subjected to bending stresses. This strength of a beam, which will hereinafter be referred to as the usable strength is a function of its elastic limit and yield point, because once the beam is stressed beyond its elastic limit, a permanent set occurs therein and the beam sags and therefore fails to perform its intended function.

Numerous patents and publications of recent years have described various cold-working methods for increasing the strength of austenitic steels. A typical example of such disclosure is to be found in U. S. Patent 1,929,356, issued October 3, 1933, to Emanuel Janitsky. In this patent however, the increase in elastic limit and strength is obtained by creating, by cold working, a partly martensitic structure which is dispersed through the austenite. This phenomenon which is manifested during the cold working of an austenitic steel will not occur in the treat- 35 ment of all ferrous metals but only in those possessing an austenitic structure. It is also a known expedient both in the ferrous and non-ferrous metal working arts to colddraw or otherwise mechanically treat shaped 40 metal articles for the purpose of increasing the density of the metal so as to secure an improved bonding between the grains of the metal and,

thus to improve its mechanical properties.

Beams, girders, and similar shaped steel articles, 45 usually known as shapes in the steel trade,

however, are usually not of an austenitic structure but are generally composed of a low carbon steel, often of sorbitic or troositic nature, and

are not amendable to the treatments proposed 50 by the prior art.

It is an object of the present invention to provide a method of treating a formed structural member by introducing stresses of such magnitude and direction as will increase the elastic- 65 limit and yield point of the metal and thereby improve the service or usable qualities of the" said member.

It is another object of the present invention to produce a metal beam which has been cold worked in compression in that portion of the 5 beam which in service will be subjected to external compressive stresses, and cold worked in tension in that portion of the beam which in, service will be subjected to external tensile stresses.

A still further object of the invention is to increase the usable strength of a metal beam, bar,

or the like, by subjecting the metal shape or formed member to a bending procedure and then straightening it while cold, thereby introducing is internal compressive stresses of greater magnitude than the elastic limit of the metal on one side of its neutral axis and introducing internal tensile stresses of greater magnitude than the elastic limit of the metal on the other side of 380 this axis.

When certain types of steel are so treated it is found expedient to subject the shape or formed member, e. g. beam, girder, etc., to a very mild 4 tempering operation after it has been cold worked; v This mild tempering, which is preferably effected by immersion in a liquid having a. temperature of about 212 F. for minutes, serves to remove any residual undesired critical stresses and thereby additionally increases the 30 elastic limit and yield point of the steel. The method is not limited to the treatment of steel beams, but is applicable to other metals having stress-strain characteristics similar to those of the various forms of known steels or having a 3'5 stress-strain curve of the same characteristics as a steel.

Other objects and features of this invention will become apparent in the course of the following description taken in the conjunction with the accompanying drawing and the invention will be defined in the claims hereto appended.

In the drawing:

Fig. 1 is illustrative of one method for eifecting the initial bending of a shaped object or shape", here shown as a beam. The beam is shown leaving the bending rolls in a permanently set, deformed condition. V

Fig. 2 illustrates a method of straightening the beam after it has been deformed by the rolls .shown in Fig. 1.

Fig. 3 is a graph showing the stress-strain curves of the same beam beforeand after treatment by the cold working method of the present invention. '86

Referring more in detail to Fig. 1, the beam l is first passed through a deforming means represented, by a set of rolls 2, 3, in such a manner that the upperflange 6 of the beam is stressed in compression beyond the elastic limit of the metal and the lower flange 1 is stressed in tension beyond the elastic limit of the metal and the beam thereby leaves the rolls 2 and 3 in a curved permanently set condition. In one form of the present invention the beam may be passed through these rolls as the last hot pass in the rolling mill and therefore, although it leaves the rolls in a curved, permanently set condition, there is a minimum of internal stresses in each flange. But it is to be understood that the method of the invention may be practised separate and apart from the rolling mill per se and that the initial deformation may be effected either hot or cold. When some types of metals such as low carbon, low alloy steels are treated, the beam may be passed through these rolls in such a manner as to receive its entire initial bending in one pass. When treating less malleable and less ductile metals it is sometimes necessary to effect the total initial deformation by passing the beam through rolls so at first to introduce a small deformation and then through additional rolls so as progressively to increase this deformation by increments until the total initial deformation desired is reached. An immersion or soak in boiling water between passes may be used when cold working a metal beam, in which the ductility or malleability of the metal is of such value as to make this mild tempering desirable.

Fig. 2 shows the cold pass through straightenrolls 4 and 5. After leaving these rolls the beam is straight and the upper flange 6 now has been stressed beyond the elastic limit in tension while the lower flange I has been stressed beyond the elastic limit in compression.

In the straightening operation, just as in the bending operation, the entire deformation neednot necessarily be effected by'one pass through the rolls but may be effected by progressive increments. A mild tempering may also be used between the progressive straightening increments and also after the final straightening operation if the metal has such properties as would make this mild tempering desirable.

If the beam is destined to be used in a strucs ture where the conditions are such that the flange 6, which was stressed beyond the elastic limit in tension in the straightening operation, is stressed in tension, and the flange I, which was stressed beyond the elastic limit in compression in the straightening operation, is stressed in compression, the usable strength of the beam will be materially increased. Tests show that loads applied in service must be such that their bending moment exerted on the beam will exceed the bending moment imposed on the beam by the straightening rolls before the metal will reach its new yield point and assume permanent set.

Fig. 3 is a graph showing results of tests made on a steel I beam treated by the method of the invention. The increase in elastic limit and yield point thus obtained are clearly shown. Curve! shows the stress-strain relationship of the original beam, the elastic limit II and the yield point l2 being those which would determine the usable strength of the beam as manufactured according method of the present invention with the mild tempering operation omitted. An increase of 44 per cent in the elastic limit l3 and hence in the usable strength of the beam is found to result from the cold working of the beam, and the yield point is found to correspond approximately to the load which was applied in the final cold straightening operation.

The preferred form of this invention includes a mild tempering operation. The stress-strain relationship of the same beam after it has been treated by this preferred form of the invention is shown by the curve II). An increase of 67 per cent in the elastic limit 11 and hence in the usable strength of the beam is found to result from the cold working and subsequent mild tempering of the beam. The yield point I6 is found to be lncreased to above the value of the load which was applied in the final cold straightening operation.

Although a preferred form of the invention and the product resulting therefrom have been described and illustrated herein, it will be apparent that the invention may be practised in other ways without departing from the spirit thereof or the scope of the appended claims. For example, the introduction of the desired stresses may be effected by any of the usual methods suitable for introducing internal tensile or compressive stresses and including such operations as hammering, pressing, unequal quenching, etc., whereas rolling is merely one readily'effected preferred form of effecting the deformation.

We claim:

1. A method of treating non-austenitic steel shapes consisting in first bending said steel shape while hot so that the longitudinal axis of said shape will describe a. curve lying in the plane in which loads will normally be applied when the shape is used for its intended purpose, and having its center of curvature on the side of the shape opposite to that where said loads will be normally applied, followed by cooling the shape to a cold working temperature, and thenstraightening said steel shape, the curvature before straightening being such that when said steel shape is cooled to a cold working temperature and straightened the internal stresses set up during the straightening operation, compressive on that side of Tthe neutral axis farthest from this. former center of curvature and tensile on that side of its neutral axis nearest to this former center of curvature ,will be in excess of the elastic limit of the material in said steel shape. I

2. A method of treating non-austenitic steel shapes as claimed in claim 1 in which the shape is stressed during the straightening operation greatest in that portion of the shape which in service will be subjected to the greatest external stresses.

3. A method of treating nonaustenitic steel shapes consisting in first bending said steel shape so that the longitudinal axis of said steel shape will describe a curve lying in the plane in which loads will normally be applied when the shape is used for its intended purpose and having its center of curvature on the side of the shape opposite to that where said loads will normally be applied and then straightening said steel shape cold followed by tempering at a temperature below that temperature which would remove all the internal stresses the curvature before straightening being such that while said metal shape is being straightened the internal stresses set up compressive on that side of the neutral axis farthest from this former centerof curvature and tensile on that side of its neutral axis nearest to this former center of curvature will be in excess of the elastic limit of the steel in said shape.

4. A method of treating non-austenitic steel shapes consisting in first bending a steel shape by hot rolling then straightening said steel shape by cold rolling followed by tempering at a temperature below that temperature which would remove all the internal stresses the curvature.

greatest in that portion of the shape which inv service will be subjected to the greatest external stresses.

6. A method of treating non-austenitic steel 1 shapes, consisting of first bending said shape, then tempering said shape at a temperature above 800 degrees F. while in a bent condition, followed by straightening said steel shape, the curvature before straightening being such that while the steel shape is being straightened the internal stresses set up, compressive on one side of the shape, and tensile on the other side, will be in excess of the elastic limit of the metal in said shape.

7. A method of treating non-=austenitic steel shapes as claimed in claim 6 in which the shape is stressed, during the straightening operation, greatest in that portion of the shape which in service will be subjected to the greatest external stresses. l

8. A method of treating non-austenitic steel shapes as iilaimed in claim 3 in which the shape is stressed during the straightening operation greatest in that portion of the shape which in service will be subjected to the greatest external stresses.

9. A methodof treating non-austenitic steel shapes consisting in setting up internal tensile and compressive stresses by bending and cold straightening followed by mild tempering, said stresses being of greater magnitude than the elastic limit of the steel in said-shapes, and in such direction that the external stresses in service must exceed these internal stresses set up during the straightening operation before the steel shape will be permanently deformed, in which the initial flexures of the difi'erent sections of the beam areproportional to the stresses which these sections will receive in service.

10. A method of treating non-austenitlc steel shapes, consisting of first bending said shape,

then tempering said shape at a temperature above 800 degrees F. while in the bent condition, followed by straightening said steel shape and tempering it at about 212 degrees F., the curvature before straightening being such that while the steel shape is being straightened the internal stresses set up, compressive on one side of the shape, and tensile on the other side, will be in excess of the elastic limit of the metal in said shape, in which the shape is stressed, during the 

